Pyrolysis of wood to produce charcoal has been accomplished throughout the world since ancient times. Pyrolysis of coal to manufacture coke has been carried out in modern times. Coal is formed from a biomass which has undergone decomposition and compacting. Coal (fossil fuel) deposits are found in almost every state in the union and are expected to provide plentiful supplies of coal for centuries to come. Both biomass and coal are carbonaceous solids that contain energy derived from the sun. There is an increasing interest in converting renewable biomass to usable products to avoid consumption of non-replaceable fossil fuels. Biomass is associated with non-fossil organic materials that contain fundamental energy derived from the sun. A biomass is often selected from the group consisting of wood, waste paper and municipal solid waste including an individual or a combination of these materials. Conversion of biomass to practical non-stationary fuels is desired. Present day interest in biomass is to provide an alternative fuel source to avoid dependence on unreliable imported petroleum crude oil for fuels.
Manufacture of water gas, as described in Chemical Engineers Handbook third edition, edited by John H Perry, pages 1579-1580, begins with coal or coke as a source of carbon transported to a steel shell about 3 to about 10 ft. diameter lined with insulation and fire brick. The coal or coke is dependent on oxygen in air for combustion to form incandescent carbon. As soon as the carbon bed obtains satisfactory temperature the air supply is shut off and steam is admitted to produce the desired water gas. The admitted steam rapidly reduces the carbon bed temperature. The steam flow is then discontinued and air flow is admitted to the steel shell to raise the carbon temperature to incandescence thus repeating the sequence. Accordingly water gas is produced. New developments for employment of low cost tonnage oxygen is being investigated for use in continuous water gas manufacture as reported by Perry, et. al.
A present day continuous process for biomass gasification is being developed at the University of Hawaii and is illustrated and explained by xe2x80x9cBiomass Gasificationxe2x80x9d on the internet. The process employs oxygen and biomass to produce water gas converted by steam to manufacture synthesis gas. The synthesis gas is then transformed from a gas to form liquid methanol. xe2x80x9cBioethanol Technologyxe2x80x9d, reported on the internet buy researchers at NREL, synthesis gas from biomass can be fermented by anaerobic bacteria to convert synthesis gas to form ethanol. Synthesis gas, containing carbon monoxide, is usually derived from petroleum materials contained in crude oil or from other non-replaceable fossil fuels.
It is therefore an object of this invention to obviate many of the limitations or disadvantages of the prior art.
A principal object of this invention is to produce carbon monoxide obtained from carbonaceous solids.
A distinct object of this invention is to employ carbon from pyrolysis of carbonaceous solids.
A further object of this invention is to create synthesis gas.
Another object of this invention is to supply thermal energy to a heat exchanger with flue gas to heat a mixture of carbon monoxide and carbon dioxide to provide energy to carbon.
Furthermore a fundamental object of this invention is to remove sensible heat from flue gas attained from combustion to generate steam.
Still another object of this invention is to make use of a flue gas to function as a dryer to remove moisture from carbonaceous solids and produce a supply of significantly moisture free carbonaceous solids for pyrolysis.
Yet another object of this invention is to provide a solution capable of combining with carbon dioxide.
An additional object of this invention is to provide carbon dioxide, separated, from a solution containing combined carbon dioxide. With the above and other objects in view, this invention relates to the novel features and alternatives and combinations presently described in the brief description of the invention.
A principle, applied in the present invention, employs carbon to react with carbon dioxide to form carbon monoxide. The chemical formula, CO2+C=2CO is provided in Chemical Process Industries, second edition, authored by R. N. Shreve, page 121. This reaction is endothermic and requires energy from an external source to maintain temperature of the carbon. Sensible heat from a heated mixture of carbon dioxide and carbon monoxide will supply energy to maintain temperature of the carbon to compensate for the energy required to form carbon monoxide by reaction of carbon dioxide. Notice that carbon monoxide in the mixture supplies sensible heat to carbon without participating in the reaction. Equilibrium of this reaction with carbon, at different temperatures, is presented in a table on pages 736 and 737 in Rogers"" Industrial Chemistry, sixth edition, volume one.
Shifting a gas containing carbon monoxide is customarily achieved with water or steam to shift carbon monoxide to carbon dioxide and hydrogen. Steam is reacted with carbon monoxide to convert carbon monoxide to carbon dioxide and hydrogen, as described by Shreve, op. cit., page 136. Also water, implied by Shreve, (assumed to be in the form of steam) is reacted with carbon monoxide to shift carbon monoxide to carbon dioxide and form hydrogen, in the chemical formula, H2O+CO=CO2+H2 presented by Shreve op. cit., page 121.
An illustration of a salt being employed to form a bicarbonate is described by Shreve, op. cit., on pages 126 and 128 in which sodium carbonate reacts with gaseous carbon dioxide and water to reversibly form water soluble sodium bicarbonate presented in the equation Na2CO3+CO2+H2O2Na HCO3. The solution containing sodium bicarbonate is then heated to reverse the reaction and concentrated carbon dioxide is produced and a solution containing sodium carbonate to be recycled. A typical example of forming a bicarbonate from a salt reacting with gaseous carbon dioxide furnished by a flue gas is thus provided. Shreve, op. cit., pages 130-132. describes a method to absorb gaseous carbon dioxide in a basic aqueous solution of potassium carbonate or mono ethanolamine in which the absorbed carbon dioxide is removed from the aqueous solution to produce carbon dioxide as a gas. A basic solution capable of reacting with carbon dioxide is often selected from the group consisting of aqueous bases and aqueous salts including an individual or a combination of these aqueous solutions thereof.
The present invention in its broadest aspect, establishes a method to produce carbon monoxide derived from carbon dioxide and carbon. A supply of carbon dioxide is advanced to carbon to react and form carbon monoxide and then separating the carbon monoxide from the carbon. Components remaining from forming carbon monoxide from carbon contain inorganic and organic components and are separated from the carbon. The separated components are subjected to combustion to form a flue gas and a residue containing inorganic components. Following separation from combustion, the residue is used to heat air for combustion. Combustion produces a flue gas to generate steam and a residue for disposition. Combustion is accomplished in a boiler provided with a heat exchanger, employing flue gas from combustion, for heating a mixture of carbon monoxide and carbon dioxide which is advanced to provide energy to carbon. The heated mixture reacts with the carbon to form carbon monoxide. The carbon monoxide, removed from the carbon, is reacted with steam to form a gaseous mixture of carbon dioxide, hydrogen and carbon monoxide which is a synthesis gas.
A basic solution capable of combining with carbon dioxide is employed to remove carbon dioxide from the gaseous mixture to provide a synthesis gas containing hydrogen and carbon monoxide substantially free of carbon dioxide and a separated solution containing combined carbon dioxide. The solution, containing combined carbon dioxide freed from the synthesis gas, is released from carbon dioxide to form gaseous carbon dioxide and a basic solution capable of combining with carbon dioxide. Pyrolysis, utilizing flue gas, is employed to provide a supply of carbon. Flue gas containing carbon dioxide is commingled with a basic solution capable of combining with carbon dioxide to form a solution containing combined carbon dioxide freed from the flue gas. The solution then releases gaseous carbon dioxide and forms a solution capable of combining with carbon dioxide.
Characteristics of the invention include:
Flue gas, derived from combustion, is employed to heat a mixture of carbon dioxide and carbon monoxide to maintain temperature of the carbon.
Thermal sensible heat from the flue gas is used to generate steam.
Carbonaceous solids are substantially dried by the flue gas to provide substantially dried carbonaceous solids subjected to pyrolysis.
Production of a synthesis gas substantially free of carbon dioxide.